Inkjet-imageable lithographic printing members and methods of preparing and imaging them

ABSTRACT

Lithographic printing plates are imaged using an inkjet printer to imagewise apply a chemical or masking agent onto the plate surface. In some embodiments, the chemical causes an affinity change, thereby facilitating lithographic printing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefits of U.S. ProvisionalApplication Ser. No. 60/617,695, filed on Oct. 12, 2004, the entiredisclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates in general to lithography, and moreparticularly to lithographic printing members suitable for inkjetimaging.

BACKGROUND OF THE INVENTION

In offset lithography, a printable image is present on a printing memberas a pattern of ink-accepting (oleophilic) and ink-rejecting(oleophobic) surface areas. Once applied to these areas, ink can beefficiently transferred to a recording medium in the imagewise patternwith substantial fidelity. Dry printing systems utilize printing memberswhose ink-repellent portions are sufficiently phobic to ink as to permitits direct application. In a wet lithographic system, the non-imageareas are hydrophilic, and the necessary ink-repellency is provided byan initial application of a dampening fluid to the plate prior toinking. The dampening fluid prevents ink from adhering to the non-imageareas, but does not affect the oleophilic character of the image areas.Ink applied uniformly to the printing member is transferred to therecording medium only in the imagewise pattern. Typically, the printingmember first makes contact with a compliant intermediate surface calleda blanket cylinder which, in turn, applies the image to the paper orother recording medium. In typical sheet-fed press systems, therecording medium is pinned to an impression cylinder, which brings itinto contact with the blanket cylinder.

Lithographic plates can be fabricated in various ways, ranging fromtraditional manual techniques involving photoexposure and chemicaldevelopment to automated procedures involving computer control.Computer-to-plate systems can utilize pulses of electromagneticradiation, produced by one or more laser or non-laser sources, to createphysical or chemical changes at selected points of sensitized plateblanks (which, depending on the system, may be used immediately orfollowing conventional photodevelopment); ink-jet equipment used toselectively deposit ink-repellent or ink-accepting spots on plateblanks; or spark-discharge equipment, in which an electrode in contactwith or spaced close to a plate blank produces electrical sparks toalter the characteristics of certain areas on a printing surface,thereby creating “dots” which collectively form a desired image. Tocircumvent the cumbersome photographic development, plate-mounting, andplate-registration operations that typify traditional printingtechnologies, practitioners have developed electronic alternatives thatstore the imagewise pattern in digital form and impress the patterndirectly onto the plate.

Digital imaging of printing plates by inkjet printing is currentlywidely investigated; see, e.g., U.S. Pat. Nos. 6,526,886 and 6,691,618.The '618 patent, for example, discloses a method of imaging alithographic printing plate having an alkaline-soluble polymeric coatingwith a pH-elevating agent. The need to use alkaline solutions to developthese plates, however, poses environmental and safety problems. It wouldbe desirable to have inkjet-imageable lithographic printing plates thatdo not require a development step.

SUMMARY OF THE INVENTION

The present invention relates to inkjet-imageable lithographic printingmembers that do not require development. In general, a printing memberin accordance with the invention includes a substrate, an optionalintermediate layer, and a reactive top layer thereover. The top layer iscapable of absorbing an inkjet imaging fluid that reacts with the toplayer to alter the affinity thereof. The optional intermediate layer canbe hydrophilic or oleophilic (but is generally hydrophilic), and may becrosslinked to improve wear resistance. An advantage of this approach isstructural and process simplicity, since imaging is accomplished bychemical modification of an existing layer. There is no need forexposure to an energy source, and imaging is effectively accomplished ina single step.

Accordingly, the invention provides a lithographic printing memberhaving a crosslinked and hydrophilic top layer and a substratethereunder, as well as methods of imaging such a printing member. Toprovide a lithographic image, an oleophilizing imaging fluid isdispensed in an imagewise pattern onto the hydrophilic top layer,transforming the imaged portions of the top layer from a hydrophilicstate to an oleophilic state. The imaged plate may be used on a pressdirectly after imaging without a development step.

Suitable materials for preparing the hydrophilic top layer includehomopolymers and copolymers having at least one of an amine moiety, acarboxylic acid moiety, a sulfonic acid moiety, and a phosphonic acidmoiety. A polyceramic layer containing PVOH—ZrOH can also be used.Imaging fluids that can oleophilize these materials include variousesterifying agents and alkylating agents, examples of which include, butare not limited to, tetramethylammonium hydroxide,phenyltrimethylammonium hydroxide, trimethylsulfonium hydroxide,trimethylsulfoxonium hydroxide, 1,3-(bistripropylammonium) xylenehydroxide, and polymers comprising quaternary ammonium salts.

It should be stressed that, as used herein, the term “plate” or “member”refers to any type of printing member or surface capable of recording animage defined by regions exhibiting differential affinities for inkand/or fountain solution. Suitable configurations include thetraditional planar or curved lithographic plates that are mounted on theplate cylinder of a printing press, but can also include seamlesscylinders (e.g., the roll surface of a plate cylinder), an endless belt,or other arrangement.

Furthermore, the term “hydrophilic” is used in the printing sense toconnote a surface affinity for a fluid which prevents ink from adheringthereto. Such fluids include water for conventional ink systems, aqueousand non-aqueous dampening liquids, and the non-ink phase of single-fluidink systems. Thus a hydrophilic surface in accordance herewith exhibitspreferential affinity for any of these materials relative to oil-basedmaterials.

The term “fountain solution,” as used herein, pertains to a solutionused to clean or remove the water-soluble portions of the imagedprinting members of the methods of this invention and may be water,combinations of at least 90% water and 10% or less organic solvents andadditives such as alcohols, surfactants, and glycols, and buffered orsalt-containing neutral or nearly neutral water solutions. The term“fountain solution,” as used herein, does not include alkaline aqueoussolutions with a pH of greater than about 10, acidic aqueous solutionswith a pH of less than about 3.5, or organic solvents without at least90% by weight of water present.

Also, as used herein, the term “water-soluble” refers to a material thatcan form a greater than 1% solution in water or a mixture of awater-miscible solvent such as alcohol and water wherein the mixture ismore than 50% water.

As one of skill in the art will appreciate, features of one embodimentand aspect of the invention are applicable to other embodiments andaspects of the invention. The above-discussed and other features andadvantages of the present invention will be appreciated and understoodby those skilled in the art from the following detailed description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing discussion will be understood more readily from thefollowing detailed description of the invention when taken inconjunction with the accompanying drawings.

FIG. 1 is an enlarged sectional view of an embodiment of anegative-working printing member according to the invention thatcontains substrate and a crosslinked hydrophilic top layer.

FIGS. 2A-2C are enlarged sectional views of the negative-workingprinting member of FIG. 1 illustrating an imaging mechanism according tothe invention.

The drawings and elements thereof may not be drawn to scale.

DETAILED DESCRIPTION OF THE INVENTION 1. Imaging Apparatus

An imaging apparatus suitable for use in conjunction with the presentprinting members includes at least an inkjet printer. To facilitateaccurate imaging of the printing members according to the invention, thepaper-handling or substrate-handling subsystem of the inkjet printershould have a short, straight paper path. A printing plate is generallystiffer and heavier than the paper or media typically used incommercially available inkjet printers. If the construction of theprinter requires the printing plate to be bent before or after it ispresented to the imaging print head, then the movement of the printingplate through the printer may not be as accurate as the media for whichthe printer was designed. Printers such as the EPSON STYLUS COLOR 3000(available from Epson America, Inc., Long Beach, Calif.) have a suitablyshort, straight paper path. A platen is preferably placed at theentrance to the paper feed mechanism. The platen may have a registrationguide rail to support the plate as it is pulled into the printer by thefeed mechanism, facilitating the accurate transport of the plate underthe imaging print head.

2. Inkjet Printing Process

Inkjet printing involves projecting tiny drops of ink fluid directlyonto the plate surface without physical contact between the inkjetprinter and the plate. The inkjet printer stores electrical datacorresponding to the image to be printed (specifically, the image orbackground area, depending on whether the plate is positive-working ornegative-working), and controls a mechanism for ejecting ink dropletsimagewise onto the plate. Printing is performed by moving the print headacross the plate or vice versa.

There are generally two mechanisms that commercially available inkjetprinters utilize to control how ink droplets are jetted. In continuousinkjet printing, the print head propels a continuous stream of inkthrough a nozzle. This stream is broken down into identical droplets,which are then selectively charged. Depending on the construction of theprinter, either the charged or the uncharged droplets are deflected andguided towards the receiving medium. The undeflected droplets arecollected and recycled. Continuous inkjet printers require complexhardware, but they offer high speed printing as an advantage.

In drop-on-demand inkjet printers, ink droplets are generated andejected through the orifices of the print head only as needed. Somedrop-on-demand systems use a thermal process to create the pressurerequired to eject ink droplets. These thermal jet (or bubble jet)printers use heat to generate vapor bubbles in a volatile component ofthe ink fluid. As these bubbles build up pressure and vaporize, inkdroplets are jetted out of the print head one at a time. Otherdrop-on-demand systems utilize a piezoelectric actuator to eject inkdroplets. In these printers, a computer signal imposes an electricalpotential across a piezoelectric material which causes it to deform. Inkdroplets are ejected as the piezoelectric material deforms and returnsto its normal dimensions. Although drop-on-demand inkjet printers haverelatively slow printing speed, they offer small drop size and highlycontrolled ink droplet placement.

The imaging step according to the invention can be performed by anysuitable inkjet printers and techniques described above. Commerciallyavailable drop-on-demand models are preferred, however, because of theirdurability and high resolution.

3. Lithographic Printing Members

A representative printing member according to the invention includes asubstrate, an optional intermediate layer, and a top layer. As shown inFIG. 1, a negative-working printing member 100 according to theinvention includes a substrate 102 and a crosslinked hydrophilic toplayer 106 that is chemically reactive with an inkjet imaging fluid 108(see FIGS. 2A-2C). Each of these layers and their functions will bedescribed in detail below.

3.1. Substrate 102

The substrate provides dimensionally stable mechanical support to theprinting member. The substrate should be strong, stable and, preferably,thin and flexible. One or more surfaces of the substrate can be eitherhydrophilic or oleophilic. Suitable substrate materials include, but arenot limited to, metals, polymers, and paper.

Metals suitable for use in substrates according to the inventioninclude, but are not limited to, aluminum, zinc, steel, chromium, andalloys thereof, which may have another metal (e.g., copper) plated overone surface. Metal substrates can have thicknesses ranging from about 50μm to about 500 μm or more, with thicknesses in the range of about 100μM to about 300 μm being preferred.

One or more surfaces of a metal substrate may be anodized. Anodizingincreases the hardness and abrasion resistance of the metal surface,which improves the mechanical strength of the substrate. The anodiclayer can also control dissipation of heat into the substrate, thusincreasing the imaging efficiency of the printing member. An anodizedaluminum substrate consists of an unmodified base layer and a porous,anodic aluminum oxide coating thereover. The anodized aluminum surfaceis hydrophilic; however, without further treatment, the oxide coatingwould lose wettability due to further chemical reaction. Anodizedsubstrates are, therefore, typically exposed to a silicate solution orother suitable reagent (e.g., a phosphate reagent) that stabilizes thehydrophilic character of the plate surface. In the case of silicatetreatment, the surface may assume the properties of a molecular sievewith a high affinity for molecules of a definite size andshape—including, most importantly, water molecules.

A preferred substrate is an anodized aluminum plate with a low degree ofgraining and an anodic layer having a thickness between about 0.5 μm andabout 3 μm (available, for example, from Precision Lithograining Corp.,South Hadley, Mass.). Graining can be achieved by methods known in theart such as by means of a wire brush, a slurry of particulates or bychemical or electrolytic means.

Polymers suitable for use in substrates according to the inventioninclude, but are not limited to, polyesters (e.g., polyethyleneterephthalate and polyethylene naphthalate), polycarbonates,polyurethane, acrylic polymers, polyamide polymers, phenolic polymers,polysulfones, polystyrene, and cellulose acetate. A preferred polymericsubstrate is a polyethylene terephthalate film such as MYLAR and MELINEX(available from E.I. duPont de Nemours Co., Wilmington, Del.).

Polymeric substrates can be coated with a transition layer to improvethe mechanical strength and durability of the substrate and/or to alterthe hydrophilicity or oleophilicity of the surface of the substrate. Ahydrophilic transition layer may include porous materials with oxygenfunctional groups at the surface. The addition of hydrophilic fillerssuch as, for example, silica particles, also enhances the hydrophilicityof the transition layer. Examples of suitable materials for hydrophilictransition layers according to the invention include proprietary hardcoat materials supplied by Bekaert Specialty Films, LLC (San Diego,Calif.). Other suitable formulations and application techniques fortransition layers are disclosed, for example, in U.S. Pat. No.5,339,737, the entire disclosure of which is hereby incorporated byreference.

Polymeric substrates can have thicknesses ranging from about 50 μm toabout 500 μm or more, depending on the specific printing memberapplication. For printing members in the form of rolls, thicknesses ofabout 200 μm are preferred. For printing members that include transitionlayers, polymer substrates having thicknesses of about 50 μm to about100 μm are preferred.

A wide variety of papers may be utilized as a substrate. Typically,papers are saturated with a polymeric treatment to improve dimensionalstability, water resistance, and strength during wet lithographicprinting.

Because the plate does not require development, it is generallypreferable to provide a substrate and an imaging layer, i.e., the toplayer, of like affinities to promote adhesion. If an intermediate layeris employed, it is preferably hydrophilic, i.e., has a lithographicaffinity opposite to that of the reacted top layer. It is generallypreferable to provide a substrate and an intermediate layer of likeaffinities to promote adhesion and to accommodate damage to theintermediate layer without loss of performance. Specifically, eventhough the intermediate layer is typically not soluble in aqueoussolutions and is not removed during the imaging process, it can still bescratched or damaged during the printmaking process. A substrate of likeaffinity will accept or reject ink in the same manner as the overlyingintermediate layer in those areas where the intermediate layer isdamaged, thus maintaining print quality and prolonging the press life ofthe printing member.

3.2 Intermediate Layer 104

The intermediate layer is coated on the substrate. In embodiments wherea polymeric substrate is used, the intermediate layer can be thetransition layer described above. The intermediate layer can be eitherhydrophilic or oleophilic, provided that it has an affinity opposite tothat of the top layer after the top layer has reacted with the imagingfluid for at least one of ink and a liquid to which ink will not adhere.It should generally adhere well to the substrate and to the top layerand should withstand repeated application of fountain solution or inkduring printing without substantial degradation or solubilization. Theintermediate layer is optional in some embodiments.

Suitable materials for fabricating a hydrophilic intermediate layerinclude, but are not limited to, polyvinyl alcohol, polyacrylamide,polyvinyl pyrrolidone, and cellulosics. Polyvinyl alcohol is preferred.Homopolymers and copolymers with amine, carboxylic acid, sulfonic acid,and/or phosphonic acid moieties can also be used. Specific examplesinclude homopolymers and copolymers of vinyl alcohol withamino-functional groups, vinyl phosphonic acid, acrylamide, methylolacrylamide, methylol methacrylamide, acrylate acid, methacrylate acid,hydroxyethyl acrylate, hydroxyethyl methacrylate, and maleicanhydride/vinylmethylether copolymers. A polyceramic layer containingPVOH—ZrOH (see, e.g., U.S. Pat. Nos. 6,182,569, 6,182,570, and6,186,067) can also be used.

To increase toughness and wear resistance, the hydrophilic polymercoating is preferably crosslinked. Crosslinking agents such asformaldehyde, glyoxal, polyisocynate, melamine-type crosslinkers,ammonium zirconyl carbonate, titanate crosslinkers, hydrolyzedtetraalkylorthosilicate, and diepoxide crosslinkers can be added tocrosslink specific functional groups in the polymer. For example,diepoxide crosslinkers can effectively crosslink amino groups andcarboxylic acid groups. Polyvinyl alcohol can be crosslinked byhydrolyzed tetraethoxysilane according to procedures described in U.S.Pat. No. 3,971,660, by ammonium zirconium carbonate as described in U.S.Pat. No. 6,490,975, and by melamine with a catalyst such as an organicsulfonic acid.

The mechanism of the crosslinking reaction is not important. Forexample, either radical-initiated crosslinking or oxidative crosslinkingmay be used.

In embodiments of the invention that include an oleophilic intermediatelayer, the materials used in the oleophilic coating should demonstrategood adhesion to the substrate below it and to the hydrophilic coatingthat is to be applied on top of it. Their oleophilic properties shouldbe such that, when placed on a press, the imaged areas accept inkimmediately. Run lengths in the order of thousands of impressions arepreferred. The oleophilic materials should therefore have suitabletoughness, wear resistance, and be non-reactive with the ink.

Many homopolymers and copolymers can be used as the oleophilicintermediate layer according to the invention. They includepolyurethanes, epoxy resins, polystyrene, copolymers of styrene,acrylics, copolymers of acetate and ethylene, polyacrylics, copolmyersof acrylics, polyvinyl acetate, phenol and cresol formaldehyde resins,cellulose ethers and esters, polyvinyl acetals, diazo resins, andsynthetic rubbers. They can be applied from a solvent solution, or canbe used in the form of an aqueous resin dispersion and be applied fromwater. Intermediate layers made from aqueous resin dispersions can beheat-treated to cause the dispersed resin particles to coalesce, whichincreases their toughness. In addition, commercially availablesubtractive coatings (e.g., subtractive plate NSSH manufactured byPrecision Lithograining, South Hadley, Mass.) with or without blanketlight exposure can be used as the oleophilic coating.

Other components that can be included in the intermediate layer arecolorants, plasticizers, surfactants, crosslinking agents and monomersincluding initiators. The latter two are added to increase toughness andcan be activated by either heat or light.

3.3 Top Layer 106

The top layer receives the imaging fluid. It is composed of a material,or a mixture of materials, that are permeable to and chemically reactivewith a suitable inkjet imaging fluid. The top layer captures the imageon the printing member by undergoing an affinity-altering propertychange in response to the imaging fluid. aterials forming the top layercan be applied to the intermediate layer (or, in embodiments where theintermediate layer is optional, the substrate) in any suitable mannerusing conventional coating equipment and procedures. Upon drying, thetop layer is generally at least 0.1 μm in thickness and can be as thickas 10 μm. Thus, in negative-working embodiments of the presentinvention, the top layer should be thick and substantially continuousenough to provide the desired image upon fluid application, but not sothick that the non-image areas are difficult to remove after imaging.Similarly, in positive-working embodiments of the present invention, thetop layer should not be so thick that the imaged areas are difficult toremove after imaging.

Apart from the components capable of reacting with the imaging fluid,the top layer may also contain various additives as appropriate to theapplication. For example, in embodiments where the printing member ispreferably heated to initiate or complete the chemical reaction betweenthe top layer and the imaging fluid, an infrared absorber may beincluded. Suitable infrared absorbers include infrared light-absorbingdyes or pigments that can effectively absorb radiation having awavelength of 700 to 1,500 nm. It is preferable that the dyes orpigments have an absorption maximum between the wavelengths of 750 and1,200 nm. Various infrared light-absorbing dyes or pigments aredescribed in U.S. Pat. Nos. 5,858,604, 5,922,502, 6,022,668, 5,705,309,6,017,677, and 5,677,106. Examples of useful infrared light-absorbingdyes include squarylium, croconate, cyanine (including polymethine),phthalocyanine (including naphthalocyanine), merocyanine,chalcogenopyryloarylidene, oxyindolizine, quinoid, indolizine, pyrylium,and metal dithiolene dyes. Cyanine and phthalocyanine dyes are preferredinfrared light-absorbing dyes. Examples of useful infraredlight-absorbing pigments include black pigments, metal powder pigments,phthalocyanine pigments, and carbon black. Carbon black is a preferredinfrared light-absorbing pigment. Mixtures of dyes, pigments, or bothcan also be used. The infrared light-absorbing dyes or pigments areadded in the top layer preferably at a level of 0.01 to 30% by weight ofthe top layer, more preferably at a level of 0.1 to 20% by weight of thetop layer, and most preferably at a level of 0.5 to 10% by weight of thetop layer.

The top layer may also comprise nonionic and/or amphoteric surfactants.Specific examples of the nonionic surfactant include sorbitantristearate, sorbitan monopalmitate, sorbitan trioleate, stearic acidmonoglyceride, polyoxyethylene nonylphenyl ether, and the like. Specificexamples of amphoteric surfactants include alkyldi(aminoethyl)glycine,hydrochloric acid salt of alkylpolyaminoethylglycine,2-alkyl-N-carboxyethyl-N-hydroxyethylimidazolinum betaine,N-tetradecyl-N,N-betaine, and the like.

Dyes can be added in a small amount to adjust the plate color. Specificexamples of these dyes include Oil Yellow No. 101, Oil Yellow No. 103,Oil Pink No. 312, Oil Green BG, Oil Blue BOS, Oil Blue N. 603, Oil BlackBY, Oil Black BS, Oil Black T-505 (all marketed by Chemical Industries,Co., Des Moine, Iowa), Victoria Pure Blue, Crystal Violet (C.I. 42555),Methyl Violet (C.I. 42535), Ethyl Violet, Rhodamine B (C.I. 145170B),Malachite Green (C.I. 42000), Methylene Blue (C.I. 52015), and the like.

Further, if necessary, a plasticizer may be added to impart flexibilityto the top layer. Examples of suitable plasticizers include butylphthalyl, polyethylene glycol, tributyl citrate, diethyl phthalate,dibutylphthalate, dihexyl phthalate, dioctyl phthalate, tricresylphosphate, tributyl phosphate, trioctyl phosphate, tetrahydrofurfuryloleate, an oligomer or a polymer of acrylic acid or methacrylic acid,and the like.

Specific embodiments of the top layer are discussed below.

3.4. Inkjet Imaging Fluid 108

The inkjet imaging fluid contains at least one chemical compound in itscomposition which is capable of reacting with the top layer. Thechemical compound(s) may be present in the imaging fluid in aconcentration as high as 20% or even higher by weight, but preferablyless than 5% by weight. It is also preferable, although not necessary,that the chemical compound(s) be in the form of a homogeneous solutionor a stable colloidal dispersion, so that it can pass through thenozzles of an inkjet print head.

The main liquid carrier can be water or an organic solvent orcombinations thereof. The choice of the liquid carrier depends on thespecific inkjet printer. Both aqueous-based and solvent-based fluids canbe used in the present invention depending on the inkjet technology thatis being used (i.e., piezo, thermal, bubble jet or continuous inkjet).

While water is the preferred medium for aqueous imaging fluids, theaqueous composition may comprise one or more miscible co-solvents, e.g.,a polyhydric alcohol. These co-solvents may be high-boiling humidifyingsolvents such as glycerin, propylene glycol, ethxylated glycerin,ethylene glycol, propylene glycol, diethylene glycol, triethyleneglycol, propylene glycol, dipropylene glycol, and trimethylol propane.The purpose of adding one or more high-boiling humidifying solvents isto prevent the imaging fluid from drying during idle periods which couldcause the inkjet nozzles to clog. Other high-boiling solvents can beadded to improve the solubility of the chemical compound tailored toreact with the top layer. Such solvents may include, but are not limitedto, methylpyrrolidone, propylene glycol monoethyl ether, propyleneglycol monobutyl ether, and propylene glycol ethyl ether acetate. Theamount of aqueous carrier medium in the aqueous composition may be inthe range from 30 to 99.995% by weight, preferably from 50 to 95% byweight.

Organic solvents that may be used as a carrier medium for the inkjetimaging fluid include, but are not limited to, alcohols, ketones oracetates.

As known in the art of the inkjet technology, the jet velocity,separation length of the droplets, drop size and stream stability isgreatly affected by the surface tension and the viscosity of the aqueouscomposition. Inkjet imaging fluids suitable for use with inkjet printingsystems may have a surface tension in the range from 20 to 60 dyne/cm,and preferably from 30 to 50 dyne/cm. Control of surface tensions inaqueous inkjet fluids may be accomplished by additions of small amountsof surfactants. The level of surfactants to be used can be determinedthrough simple empirical experiments. Several anionic and nonionicsurfactants are known in the inkjet art. Commercial surfactants includethe SURFYNOL series, e.g., SURFYNOL 104, SURFYNOL 45, SURFYNOL FS-80,SURFYNOL PSA-216 (available from Air Products, Allentown, Pa.); theDYNOL series, e.g., DYNOL 604 (available from Air Products, Allentown,Pa.); the TRITON series, e.g., TRITON X-100 (available from Rohm andHaas, Philadelphia, Pa.); the ZONYL series (available from E.I. duPontde Nemours Co., Wilmington, Del.); the FLUORAD series (available fromMinnesota Mining and Manufacturing Co., St. Paul, Minn.); the AEROSOLseries (available from American Cyanamid Co., Wayne, N.J.); and similarchemicals. The viscosity of the fluid is preferably not greater than 20mPA·s, e.g., from 1 to 10 mPA·s, preferably from 1 to 5 mPA·s at roomtemperature.

The inkjet imaging fluid may further comprise other ingredients. Abiocide may be added to prevent unwanted microbial growth which mayoccur in the fluid over time, and which would otherwise degrade theshelf life of the fluid. Suitable biocides include, but are not limitedto, PROXEL GXL (available from Zeneca Specialties, Manchester, UK),sodium OMADINE (available from Olin Mathieson Chemical Corp., New York,N.Y.), GIVGARD DXN (available from Givaudan Corp., New York, N.Y.),solution of 1,2-benzothiazoline-3-one, sodium hydroxide and dipropyleneglycol, 2-pyridinethiol-1-oxide, sodium salt, DOWICIL (available fromDow Chemical, Midland, Mich.),cis-1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride, andsimilar chemicals or mixtures of such chemicals. When used, the biocidewill typically be 0.1 to 3% by weight of the ink.

Additional additives that may be optionally present in the ink includethickeners, pH adjusters, buffers, conductivity-enhancing agents, dryingagents and defoamers.

Dyes may be added in order to enhance the image contrast after jettingthe image on the top layer. Many dyes and pigments are known to besuited for inkjet technology. Suitable dyes are further selected basedon their compatibility in the carrier medium (i.e., aqueous-based orsolvent-based) and on their compatibility with the reactive chemicalcompound, e.g., they should not lead to coagulation.

Specific embodiments of the imaging fluids and the compositions of thetop layers are discussed below in detail, along with the imagingtechniques associated therewith.

4. Imaging Techniques

According to the embodiment illustrated in FIG. 1, the printing member500 includes a grained, anodized, and/or silicated aluminum substrate102 and a crosslinked hydrophilic top layer 106. The top layer 106becomes oleophilic when reacted with the imaging fluid 108. Printingmember 100 may be directly run on a press without a development step.

FIGS. 2A-2C illustrate the consequences of imaging an embodiment of theprinting member 100. As illustrated in FIG. 2A, an inkjet printer 110 isused to apply droplets of the imaging fluid 108 imagewise onto thehydrophilic top layer 106. The imaging fluid 108 wets and penetrates thetop layer 106, and creates an imaged area 112. The imaged plate 100 maythen be heated, e.g., in an oven, or alternatively, by exposure to aninfrared radiation source 120, as shown in FIG. 2B. The heated fluid 108reacts with the crosslinked top layer 106 and transforms the imaged area112 of the crosslinked layer 106 from a hydrophilic state to anoleophilic state. No development step is required. The imaged plate 100may be placed on a press directly after imaging. FIG. 2C illustrates theaffinity of ink and fountain solution on the imaged plate 100 when it isrun on the press. As shown in FIG. 2C, the fountain solution 128 isrepelled by the imaged oleophilic area 112, which then accepts printingink 138.

Suitable materials for preparing the hydrophilic top layer 106 includehomopolymers and copolymers comprising amino, carboxylic acid, sulfonicacid, and/or phosphonic acid moieties. Specific examples includehomopolymers and copolymers of vinyl alcohol with amino-functionalgroups, vinyl phosphonic acid, acrylamide, methylol acrylamide, methylolmethacrylamide, acrylate acid, methacrylate acid, hydroxyethyl acrylate,hydroxyethyl methacrylate, and maleic anhydride/vinylmethylethercopolymers. A polyceramic layer containing PVOH—ZrOH (see, e.g., U.S.Pat. Nos. 6,182,569, 6,182,570, and 6,186,067) can also be used.

To increase toughness and wear resistance, the hydrophilic top layer 106is preferably crosslinked. Crosslinking agents such as formaldehyde,glyoxal, polyisocynate, melamine-type crosslinkers, ammonium zirconylcarbonate, titanate crosslinkers, hydrolyzed tetraalkylorthosilicate,and diepoxide crosslinkers may be added to crosslink specific functionalgroups in the polymer. Other methods of crosslinking that may be used toprepare the top layer 506 include, but are not limited to,radical-initiated crosslinking and oxidative crosslinking. The methodsof crosslinking, however, should not substantially change thehydrophilic nature of the polymer.

Suitable compositions for inkjet imaging fluid 108 include variousoleophilizing agents. For example, imaging fluid 108 may contain one ormore esterifying agents, examples of which include, but are not limitedto tetramethylammonium hydroxide, phenyltrimethylammonium hydroxide,trimethylsulfonium hydroxide, trimethylsulfoxonium hydroxide, and1,3-(bistripropylammonium)xylene hydroxide. Alternatively, inkjetimaging fluid 108 may contain a component for promoting anesterification and/or alkylation reaction. Preferred examples includepolymers containing quaternary ammonium salts.

It will be seen that the foregoing techniques provide a basis forimproved lithographic printing and superior plate constructions. Theterms and expressions employed herein are used as terms of descriptionand not of limitation, and there is no intention in the use of suchterms and expressions of excluding any equivalents of the features shownand described or portions thereof. Instead, it is recognized thatvarious modifications are possible within the scope of the inventionclaimed.

What is claimed is: 1-24. (canceled)
 25. A method of lithographicprinting, the method comprising the steps of: (a) providing a printingmember comprising a hydrophilic layer having an exposed surface, atleast the surface of the layer undergoing a phase change from ahydrophilic state to an oleophilic state in response to an imagingfluid; (b) dispensing the imaging fluid in an imagewise pattern, theimaging fluid chemically reacting with at least the surface of the layerand inducing the phase change, thereby creating an imagewiselithographic pattern of hydrophilic and oleophilic areas on the printingmember; (c) without developing the printing member to remove portions ofthe hydrophilic layer, sequentially applying an aqueous fluid and ink tothe printing member, whereby the ink adheres only to the oleophilicareas of the printing member; and (d) transferring the adhered ink fromthe printing member to a recording medium.
 26. The method of claim 25,wherein the top layer comprises a crosslinked hydrophilic polymer. 27.The method of claim 26, wherein the hydrophilic polymer is selected fromthe group consisting of polyvinyl phosphonic acid, polyvinyl alcoholcomprising an amine moiety, and any polymer comprising at least one of acarboxylic acid moiety, a sulfonic acid moiety, and a phosphonic acidmoiety.
 28. The method of claim 25, wherein the imaging fluid comprisesan esterifying agent.
 29. The method of claim 28, wherein theesterifying agent is selected from the group consisting oftetramethylammonium hydroxide, phenyltrimethylammonium hydroxide,trimethylsulfonium hydroxide, trimethylsulfoxonium hydroxide, and1,3-(bistripropylammonium)xylene hydroxide.
 30. The method of claim 25,wherein the imaging fluid comprises an alkylating agent.
 31. The methodof claim 25, wherein the imaging fluid comprises a quaternary ammoniumsalt.
 32. The method of claim 25, wherein the printing member furthercomprises a hydrophilic substrate beneath the hydrophilic layer.